Traces of anthrax have been discovered in a diplomatic mail pouch at the American embassy in Vienna.

A miniscule amount of the deadly spores were found in a bag shipped from Washington on 23 October, Austrian interior ministry spokesman Rudolf Gollia said.

He said the embassy was on alert, but there was no threat to the Austrian people.

No-one has been charged over the US anthrax attacks

The embassy, like other American embassies across the globe, had quarantined several mail pouches for testing as a precaution following the anthrax mail attacks in the United States, which have killed five people.

Richard Boucher, a spokesman for the US State Department, said that the bags were later released and then tested by the Austrian military.

"They informed the embassy today (Thursday) that one of them tested positive for anthrax," he said.

Embassy staff have been given antibiotics as a precaution while workers decontaminate the embassy building's mail room.

US Anthrax cases

Five fatal inhalation anthrax cases

Six recovering inhalation anthrax cases

11 recovering cutaneous anthrax cases

37 people exposed to anthrax bacteria

No staff have shown signs of infection, the embassy said.

The finding comes as US authorities remain mystified as to the source of the anthrax attacks there.

Investigators are still studying a letter sent to US Senator Patrick Leahey, which contained vast amounts of the bacteria, in the hope of picking up clues as to who is behind the attacks.

Earlier this month, investigators said the anthrax was virtually identical to a strain developed more than 30 years ago in a US military biological warfare programme that was shut down in 1969.